1. Field
Embodiments of the invention relate to the field of charging stations for electric vehicles; and more specifically, to a safety supervisory module of an electric vehicle charging station.
2. Background
Electric vehicle charging stations connect electric vehicles (e.g., electric battery powered vehicles, plug in hybrid electric vehicles, etc.) to the electric power supply network for the purpose of charging batteries (or other electrical storage devices) of electric vehicles. The charging stations may be configured for level one charging and/or level two charging. In level one charging, the charging station includes a standard electrical receptacle to accept charging cords for electric vehicles (e.g., conforming to NEMA standards 5-15, 5-20, 14-50 or other standards (e.g., BS 1363, CEE7, etc.)) and typically charges at 16 amps or less. In level two charging, the charging station includes dedicated supply equipment and has either a fixed charging cord where one end is terminated and secured at the charging station or has an electrical receptacle (e.g., conforming to one of the following standards: SAE J1772, IEC 62196-2, and IEC 60309) that allows the charging cord to be plugged and unplugged from the charging station. The other end plugs into on-board charging circuitry of an electric vehicle. In level two charging, the maximum current is typically 80 amps or less. In level two charging, a control pilot signal is sourced by the charging station and, among other things, verifies whether an electric vehicle is properly connected and is ready to accept energy.
Electric vehicle charging stations commonly are required to comply with safety regulations and standards since a dangerous amount of current may be transferred. For example, UL 2231-2 is a standard for electric vehicle supply circuits and protecting devices for use in the charging systems. UL 2231-2 requires that a supervisory circuit exist in the electric vehicle supply equipment that allows for the periodic testing of a ground fault circuit through use of a simulated ground fault, or automatically testing the system prior to each operation. The tests must also include determining whether the contacts are fused closed or shut.